Practical Wood Working

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Saturday March 25, 2017

Screw Advance Box Joint Jig


I've been making box joints (aka finger joints) for a long time using the simple table saw sled that almost everyone uses at one time or another. I like the their simplicity but they are limited in what they can do and you have to keep a keen eye out for little pieces of sawdust and chips that can get under the piece being cut. Sawdust can get under the piece because after every cut you have to lift and move it on the indexing peg.

With Matthias Wandel's Screw Andvance Box Joint Jig you can clamp all four pieces of your box into the jig (on the simple jig you usually only do 2 sides at a time), make all of your cuts, and then turn the pieces over and do the other four sides. Only when you make your second set of cuts do you need to deal with sawdust at all.

Another plus is that it is easy to make finger joints in a 2x4. Whereas finger joints are usually used for decorative pieces and boxes, this opens up a lot of possibilities for making ultra strong joints for the more utilitarian projects. Matthias makes L-shaped shelf brackets. Easy and strong!

The heart of the jig is a sliding carriage that is precisely controlled by a 3/8" x 16 piece of threaded rod. Because there are 16 threads to the inch, everytime the rod rotates it moves the carriage 1/16 of an inch. 4 rotations: 1/4". Neat.

box joint tests

One of the best things about this jig is that you can use a use any table saw blade you want to make almost any size of fingers you want. A 1/8" blade will make 1/8", 1/4", 1/2" fingers, or whatever you want.

The plans are well thought out and at $12 you get a lot for your money. The hardest part for me was making the wooden gears. But after I succeeded in making good gears I was puzzled as to why it was so hard for me. It seems so simple now.

If you start poking around on the internet you will find a lot of different types of finger joint jigs. Apparently making the better mouse trap is "a thing" with wood workers. Once I get a little time I plan on remaking the carriage using finger joints, which I obviously couldn't do until I finished the jig.

The fun never ends around here.

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